Process for nickel-cobalt separation

ABSTRACT

A method for the separation of cobalt from a mixture of certain cobalt compounds and the corresponding nickel compounds wherein the cobalt is in the cobaltous state, e.g., a mixture of cobaltous hydroxide and nickel hydroxide. The mixture is treated with a hot (above 150* F.) aqueous solution of an alkali metal hydroxide, e.g., sodium hydroxide or potassium hydroxide, containing at least 10 percent hydroxide. The cobalt compound goes into solution while the nickel compound stays in the solid phase.

United States Patent Holmes et al.

[ Feb. 15,1972

[54] PROCESS FOR NICKEL-COBALT SEPARATION [72] Inventors: Tunis L. Holmes, 1410 Warrington Road,

Deerfield, 111. 60015; Robert N. Moore, 791 Beau Drive, Des Plaines, Ill. 60016 [22] Filed: Jan. 11, 1971 [21] Appl. No.: 105,657

Related US. Application Data [63] Continuation-in-part of Ser. No. 809,943, Mar. 24, 1969, abandoned, which is a continuation-in-part of Ser. No. 721,615, Apr. 16, 1968, abandoned.

521 user ..23/l83,75/l01,7S/108,

75/119 [511 lnt.Cl...'. ..C0lg5l/04,C0lg53/04 [5s fieldot'Search ..75/10l,108,119;23/183,61

156] References Cited UNITED STATES PATENTS 2,879,137 3/1959 Bareetal ..23/183 OTHER PUBLICATIONS Mellor, Comprehensive Treatise on Inorganic and Theoretical Chemistry, Longmans, Green & Co., N.Y.. 1936, Vol. 14, p. 566 and Vol. l5,p. 382.

Primary Examiner-Hyland Bizot Assistant Examiner-43. T. Ozaki AttorneyMerriam, Marshall, Shapiro & Klose [57] ABSTRACT 13 Claims, No Drawings PROCESS FOR NICKEL-COBALT SEPARATION This application is a continuation-in-part of our copending application, Ser. No. 809,943, filed Mar. 24, 1969, now abandoned, which in turn is a continuation-in-part of our application, Ser. No. 721,615, filed Apr. 16, 1968, now abandoned.

This invention relates to the separation and separate recovery of nickel and cobalt from mixtures, compounds or alloys containing these metals'More particularly, the invention relates to such a process of separation which permits the separate recovery, on an economically feasible commercial scale, of separate nickel and cobalt fractions containing less than about 0.2 percent of the other metal.

The separation of nickel and cobalt from each other, these metals usually being found together, as in ores or alloys, has long presented a problem to the art. A number of possible solutions to this problem have been presented, of varying degrees of complexity and expense, which have permitted'the separation of nickel and cobalt into separate fractions with varying degrees of efiiciency. Some prior separation methods have achieved commercial acceptance, and generally result in a recovered nickel or cobalt fraction containing not more than about 1 percent of the other metal. Increasingly stringent requirements for these metals in commercial quantities containing not more than about 0.2 percent of the other metal as a contaminant, however, have further aggravated the severity of the separation problem. Although some methods exist for isolation of these metals in the desired standard of purity, in general these methods are complicated, expensive, and not well adapted to use on a commercial scale.

In accordance with the present invention there is provided a relatively simple process which is not only capable of achieving separation of nickel and cobalt to at least 99.8 percent purity relative to the other metal, but also is more economical than any known separation method.

The process of the invention involves the differential solubility of certain cobalt compounds relative to the corresponding nickel compounds, in hot concentrated solutions of caustic hydroxides, i.e., the hydroxides of the alkali metals.

We have found that the cobalt compounds of the invention are soluble in solutions of caustic hydroxides containing at least about percent by weight of the caustic, at temperatures ranging from about 150 F. to the boiling point of the solution under atmospheric pressure, while the corresponding nickel compounds are essentially insoluble under these conditions. Accordingly, by treating a mixture containing both a cobalt compound and a nickel compound with such a hot concentrated caustic solution, essentially all of the cobalt compound will dissolve in the treating solution leaving behind substantially all of the nickel compound as an insoluble phase.

The caustic-soluble cobalt compounds which are useful in the. invention contain cobalt in the cobaltous state (that is, with valence of +2) and fall into the following categories:

1 cobaltous hydroxide 2. cobaltous carbonate 3. cobaltous oxide 4. cobaltous salts of inorganic acids, such as cobaltous chloride, cobaltous nitrate, and cpbaltous sulfate.

5. .cobaltous ammines, i.e., ammonia complexes of cobaltous salts of inorganic acids, such as hexammine cobaltichloride and pentammine cobaltichloride.

These cobalt compounds will be referred to herein as caustic-soluble cobalt compound(s). The term nickel compound(s)" will be used to refer to the corresponding compounds of nickel.

Although the process of the invention will generally be applied to a mixture of cobalt and nickel compounds in which the anions are identical, e.g., a mixture of nickel and cobalt hydroxides or a mixture of nickel and cobalt carbonates, the invention is not so limited. Since all of the defined cobalt compounds are soluble in hot caustic solutions, while all of the corresponding nickel compounds are insoluble, any causticsoluble cobalt compound can be selectively removed from a mixture with any one or more of the nickel compounds defined above.

The process of the invention can be carried out in either of two modes, depending on the source of the mixture of nickel and cobalt to be separated. ln one variant of the invention, the nickel compound and the cobalt compound are coprecipitated as a solid phase, e. g., as the hydroxide or the carbonate, from a solution containing these metals, in a manner well known to those skilled in the art. it is possible, by this means, to separate from a solution containing many components other than nickel and cobalt, a solid fraction consisting essentially only of the nickel and cobalt content of the solution. This precipitated solid phase containing the nickel and cobalt is separated from the solution by conventional means and then treated with hot concentrated caustic solution in a manner to be described below.

The second mode of the invention can be used with a solution containing nickel and cobalt ions and no other ions which might interfere by reaction with the added hot caustic solution and cause difficulty in manipulation or further purification of the desired products. Such a starting material, for example, might be an acid solution of a nickel-cobalt alloy from which pure nickel and cobalt are to be recovered. With such a solution of nickel and cobalt it is not necessary first to precipitate a solid phase containing the nickel and cobalt. instead, a sufficient quantity of the desired caustic hydroxide is addeddirectly to the hot solution to make a mixture containing the requisite concentration of dissolved caustic hydroxide. The process then is carried out in the same manner as that described in connection with the first variant above.

In general, all of the hydroxides of the alkali metals (i.e., lithium, sodium, potassium, rubidium, and cesium) are useful in the invention. The preferred materials are sodium hydroxide and potassium hydroxide, because of their relatively low cost and efficient performance.

The caustic solutions contemplated for use in the invention contain at least about 10 percent by weight of the hydroxide. in general, the more concentrated the solution, the greater the concentration of caustic-soluble cobalt compound which will dissolve therein. On the other hand, at concentrations above about 70 percent, the solution may become excessively viscous and difficult to handle. For this reason, solutions having concentrations within the range of .20 to 70 percent are suitable and those of about 30-50 percent by weight are preferred, although more concentrated solutions and even percent caustic in molten form can be used. When highly concentrated solutions or pure caustic are used, it will 'be found convenient to cool the solution after treatment of the cobalt-nickel mixture and leach with water if the material is solid at the desired filtration temperature.

Although, as discussed below, high temperatures are necessary for dissolving the cobalt compound in the caustic solution, once dissolved, the cobalt compound will stay in solution even though the temperature is markedly reduced. Thus, for example, only about 10 percent of the dissolved cobalt present in a caustic solution at about its boiling point precipitates out of solution when the temperature is reduced to room temperature. This effect can be used to advantage by permitting filtration of the cobalt solution to be carried out at a lowered temperature, without seriously affecting the degree of cobaltnickel separation which is obtained.

The concentrated caustic solutions of the invention are used while hot and, in general, the hotter the solution the more readily soluble is the cobalt compound therein. The usable temperature range extends from about F. to the normal boiling point of the caustic solution, and a preferred temperature range is about 250300 F.

The manipulative aspects of the practice of the ,invention are simple. It is only necessary to agitate the material being treated in the presence of the hot caustic solution for l5-30 minutes, and usually not more than 3-5 minutes, whereupon the cobalt content goes into solution. Separation of the resulting liquid phase (containing dissolved cobalt) from the remaining solid phase (containing the undissolved nickel compound) can be carried out by any of the conventional methods heretofore known in the art, such as filtration, centrifuging, and the like. Depending on the efficiency of separation of the liquid phase, it may be desirable to wash the resulting solid phase with additional hot caustic solution to remove residual cobalt-containing liquor.

The process of the invention is illustrated in the following examples.

EXAMPLE 1 The starting material for this example was a nickel-cobalt hydroxide containing nickel and cobalt in a 1:1 metal content weight ratio, and a total of 2 grams of cobalt. This material was agitated with 150 ml. of a sodium hydroxide aqueous solution containing 40 percent by weight of NaOH. The treatment continued for 15-30 minutes at about 240 F.', after which the solid phase was removed by filtering under vacuum using a filter aid. The filtrate contained 6.4 grams per liter of cobalt and the ratio of nickel to cobalt in the filtrate was 0.09 to 99.91. The treatment with hot caustic was repeated eight times, after which the filter cake was analyzed and found to have a nickel-to-cobalt ratio of 99.55 to 0.45.

EXAMPLE 2 A quantity of the same nickel-cobalt hydroxide of Example 1 containing 3 grams of cobalt was treated at about 280 F., with 300 ml. of aqueous sodium hydroxide solution containing 50 percent by weight of NaOH. After filtration, the filtrate was found to have cobalt concentration of 5.4 grams per liter and a nickel-to-cobalt metal content weight ratio of 0.15 to 99.85.

EXAMPLE 3 A quantity of the nickel-cobalt hydroxide of Example 1 containing 2 grams of cobalt was treated with 200 ml. of aqueous NaOH solution containing 35 percent by weight of NaOH, at the boiling point of the solution (about 248 F.) After filtration, the filtrate was found to have a nickel-to-cobaltmetal content weight ratio of 0.08 to 99.92. The treatment with the sodium hydroxide solution was repeated twice and the resultant filter cake was washed with 2,000 ml. of hot 35 percent aqueous NaOH solution. The filter cake had a nickel-tocobalt metal content weight ratio of 99.90 to 0.10.

EXAMPLE 4 A quantity of the nickel-cobalt hydroxide of Example 1 containing 4 grams of cobalt was treated at 250 F. with 450 ml. of 40 weight percent aqueous NaOH solution. The filtrate after filtration had a cobalt concentration of 3.0 grams per liter and no detectable nickel content (i.e., less than 0.001 g./l.).

EXAMPLE 5 EXAMPLE 6 Nickel-cobalt carbonate was coprecipitated from a nickelcobalt sulfate solution using a solution of sodium carbonate. The precipitate had a 1:1 metal content weight ratio of nickel to cobalt and a total weight of 5 grams of each metal.

The precipitated carbonate was filtered, not dried, and then treated with 50 ml. of a boiling (about 284 F.) solution of sodium hydroxide containing 50 percent NaOH by weight. The. mixture wasagitated minutes, then cooled to 200 F. and filtered under vacuum without any filter aid. The filtrate contained a total of 4.5 grams of cobalt at a concentration of 9.2 g./l. and the ratio of Ni/Co in solution was 0.03/99.97.

The procedure was repeated on the filter cake an additional nine times. Analysis of the final cake showed a nickel-t0- cobalt ratio of99.2/0.8.

EXAMPLE 7 The procedure of Example 6 was repeated using nickelcobalt carbonate in which the nickel/cobalt ratio was 30/70 and the precipitate contained a total of 7 grams of cobalt. The filtrate from the first treatment with hot caustic solution contained 6.3 grams of cobalt at a concentration of 14.6 grams per liter and the ratio of nickel to cobalt was 0.0l/99.99. The treatment on the filter cake was repeated seven times giving a final nickel/cobalt ratio in the cake of 99. l /0.9.

EXAMPLE 8 Nickel sulphate and cobaltous sulfate crystals were dissolved in water to provide 500 ml. of a solution with a nickel/cobalt ratio of 1/1, containing 5 grams of cobalt. 500 grams of commercially pure sodium hydroxide were added to the solution, agitated and heated to about 280 F. for 15 minutes. After filtration, the filtrate was found to have a cobalt concentration of 5.6 grams per liter and a nickel/cobalt metal content weight ratio of 0.05 to 99.95. The filtered cake was washed seven times with the same concentration of caustic at the same temperature after which it was analyzed and found to have a nickel-to-cobalt ratio of 99.6 to 0.4.

EXAMPLE 9 Nickel chloride and cobaltous chloride crystals were dissolved in water to form a solution with a nickel/cobalt ratio of l/ l and a cobalt content of 8 grams per liter. Sufficient aqueous ammonia was added to 500 ml. of the solution (containing 4 grams of cobalt) to insure that the nickel-cobalt chloride solution was fully complexed, with the formation of ammines. 500 grams of commercially pure sodium hydroxide were added, agitated and heated to about 280 F. for 15 minutes. After filtration the filtrate was found to have concentration of 4.3 grams per liter of cobalt, and a nickel-to-cobalt metal content weight ratio of 0.08 to 99.92. The filter cake was treated with a like quantity of caustic at the same temperature and after eight repetitions was found to have a nickel/cobalt ratio of 99.6 to 0.4.

EXAMPLE 10 Approximately 25 grams each of commercially pure nickel sulfate and cobaltous sulfate were dissolved in 500 ml. of water. Sodium hydroxide was added to this solution until the pH increased to 8.0 at which point the dissolved nickel plus cobalt was coprecipitated as nickel/cobalt hydroxide. This precipitate, containing approximately 5 grams of nickel plus 5 grams of cobalt, was filtered from the solution and air dried for 72 hours. The dried mass was gradually added to approximately 500 grams of commercially pure sodium hydroxide which has been brought to a molten state by heating to a temperature greater than 620 F. The resulting solution was held at a temperature between 650 and 700 F. for a period of 10 minutes and subsequently cooled to a solid mass. The solid mass was dissolved in approximately 700 ml. of water, filtered, and the filtrate analyzed for nickel and cobalt. The filtrate was found to contain 4.1 grams of cobalt and less than 0.005 gram of nickel; a ratio of approximately 820/1 cobalt/nickel. The filtered insoluble material was washed six times with a 50 percent concentration of sodium hydroxide in water at a temperature of 280 F. after which it was analyzed and found to have a nickel to cobalt ratio of 99.7 to 0.3.

Althoughthe specific examples set forth above have only used the hydroxides, carbonates, sulfates, chlorides and ammines of nickel and cobalt, essentially similar results can be obtained with any of the caustic-soluble cobalt compounds of the invention in admixture with any nickel compound.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom as modifications will be obvious to those skilled in the art.

We claim:

l. The method of separating cobalt from a mixture of one or more of the following cobalt compounds with one or more of the corresponding nickel compounds:

1. cobaltous hydroxide;

2. cobaltous carbonate;

3. cobaltous oxide;

4. cobaltous salts of inorganic acids;

5. ammonia complexes of cobaltous salts of inorganic acids, which process comprises treating said mixture with an aqueous solution of an alkali metal hydroxide, at atmospheric pressure and at a temperature between about 150 F. and the normal boiling point of said solution, said solution consisting of water and (containing) at least about percent by weight of said hydroxide, whereby said cobalt compound goes into solution, and separating a liquid phase containing said cobalt as cobaltous ions from a solid phase containing said nickel.

2. The method of claim 1 wherein said cobalt compound is cobaltous hydroxide of cobaltous carbonate.

3. The method of claim 1 wherein said hydroxide treating solution is a solution of sodium hydroxide.

4. The method of claim 1 wherein said hydroxide treating solution is a solution of potassium hydroxide.

5. The method of claim 1 wherein said hydroxide treating solution contains about 30-50 percent by weight of said hydroxide.

6. The method of claim 1 wherein said hydroxide treating solution is maintained at a temperature within the range from about 250 to about 300 F.

7. In a method for separating nickel from cobalt, the step of forming a mixture of an alkali metal hydroxide and an aqueous solution consisting of water and (comprising) dissolved compounds of said metals, said compounds being cobaltous hydroxide, cobaltous carbonate, cobaltous oxide, cobaltous salts of inorganic acids, ammonia complexes of cobaltous salts of inorganic acids, and the corresponding nickel compounds,

in which said cobalt exists in the cobaltous state, and maintaining said mixture at atmospheric pressure and at a temperature between about F. and the normal boiling point of the mixture, said hydroxide being supplied in an amount of at least about 10 percent by weight of the resulting mixture, whereby nickel compounds are precipitated while said cobalt stays in solution as cobaltous ions.

8. The method of claim 7 wherein the amount of said hydroxide is about 30-50 percent by weight of the resulting mixture.

9. The method of claim 7 wherein said hydroxide is sodium hydroxide.

10. The method of claim 7 wherein said hydroxide is potassium hydroxide.

11. The method of claim 7 wherein the temperature of said mixture is maintained within the range of about 250300 F.

12. The method of separating cobalt from a mixture of cobaltous hydroxide and nickel hydroxide which comprises treating said mixture with a hot aqueous solution consisting of water and about 30-50 percent by weight of NaOH, said treating solution being maintained at atmospheric pressure and at a temperature of about 250300 F., whereby said cobalt hydroxide goes into solution, and separating a liquid phase containing said cobalt as cobaltous ions from a solid phase containing said nickel.

13. The method of separating cobalt from a mixture of cobaltous carbonate and nickel carbonate which comprises treating said mixture with a hot aqueous solution consisting of water and about 3050 percent by weight of NaOl-l, said treating solution being maintained at atmospheric pressure and at a temperature of about 250300 F., whereby said cobaltous carbonate goes into solution, and separating a liquid phase containing said cobalt as cobaltous ions from a solid phase containing said nickel.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 642 440 Dated February 15 1972 Inventor) Tunis L. Holmes et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, claim 2, line 18, "of" should read or Signed and sealed this 25th day ofJuly 1972.

(SEAL) Attest:

EDWARD M.ELETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM Po 1050 (10 69) V USCOMM-DC QOS'IB'POQ fi U.S. GQVERNMENT PRINTING OFFICE 19.9 O3l-J3 v mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 164L440 Dated Februarv l5 1972 Inventor) Tunis L. Holmes and Robert N. Moore It is certified that error appears in the aboveidentified patent and that said Letters Patent are hereby corrected as shown below:

Column 5, Claim 1, line 13, "(containing)" should be 7 deleted. o

Column 5, Claim 7, line 31, "(comprising)" should be deleted.

Signed and sealed this 28th day of November- 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GUTTSCHALK Attesting Officer Commissioner of Patents 

2. The method of claim 1 wherein said cobalt compound is cobaltous hydroxide of cobaltous carbonate.
 2. cobaltous carbonate;
 3. cobaltous oxide;
 3. The method of claim 1 wherein said hydroxide treating solution is a solution of sodium hydroxide.
 4. The method of claim 1 wherein said hydroxide treating solution is a solution of potassium hydroxide.
 4. cobaltous salts of inorganic acids;
 5. ammonia complexes of cobaltous salts of inorganic acids, which process comprises treating said mixture with an aqueous solution of an alkali metal hydroxide, at atmospheric pressure and at a temperature between about 150* F. and the normal boiling point of said solution, said solution consisting of water and (containing) at least about 10 percent by weight of said hydroxide, whereby said cobalt compound goes into solution, and separating a liquid phase containing said cobalt as cobaltous ions from a solid phase containing said nickel.
 5. The method of claim 1 wherein said hydroxide treating solution contains about 30-50 percent by weight of said hydroxide.
 6. The method of claim 1 wherein said hydroxide treating solution is maintained at a temperature within the range from about 250* to about 300* F.
 7. In a method for separating nickel from cobalt, the step of forming a mixture of an alkali metal hydroxide and an aqueous solution consisting of water and (comprising) dissolved compounds of said metals, said compounds being cobaltous hydroxide, cobaltous carbonate, cobaltous oxide, cobaltous salts of inorganic acids, ammonia complexes of cobaltous salts of inorganic acids, and the corresponding nickel compounds, in which said cobalt exists in the cobaltous state, and maIntaining said mixture at atmospheric pressure and at a temperature between about 150* F. and the normal boiling point of the mixture, said hydroxide being supplied in an amount of at least about 10 percent by weight of the resulting mixture, whereby nickel compounds are precipitated while said cobalt stays in solution as cobaltous ions.
 8. The method of claim 7 wherein the amount of said hydroxide is about 30-50 percent by weight of the resulting mixture.
 9. The method of claim 7 wherein said hydroxide is sodium hydroxide.
 10. The method of claim 7 wherein said hydroxide is potassium hydroxide.
 11. The method of claim 7 wherein the temperature of said mixture is maintained within the range of about 250*-300* F.
 12. The method of separating cobalt from a mixture of cobaltous hydroxide and nickel hydroxide which comprises treating said mixture with a hot aqueous solution consisting of water and about 30-50 percent by weight of NaOH, said treating solution being maintained at atmospheric pressure and at a temperature of about 250*-300* F., whereby said cobalt hydroxide goes into solution, and separating a liquid phase containing said cobalt as cobaltous ions from a solid phase containing said nickel.
 13. The method of separating cobalt from a mixture of cobaltous carbonate and nickel carbonate which comprises treating said mixture with a hot aqueous solution consisting of water and about 30-50 percent by weight of NaOH, said treating solution being maintained at atmospheric pressure and at a temperature of about 250*-300* F., whereby said cobaltous carbonate goes into solution, and separating a liquid phase containing said cobalt as cobaltous ions from a solid phase containing said nickel. 